"The history and theory of human textual indexing are surveyed. Basic terms are defined, the extent of the literature is discussed, and key concepts are explained, with an emphasis on thesaurus-based indexing. A section on the consistency of human indexing leads into a discussion of automatic indexing algorithms. An assessment of the future of human indexing concludes the entry. Pages from an early printed index and a manuscript index illustrate the structural elements of index entries as well as features of the format of early indexes that are still found in contemporary publications."